Field of the Invention
The present invention relates to a conductive polymer ink composition and an organic solar cell including the same.
Description of the Related Art
Research into conductive polymers having various applications such as fuel cells, solar cells, displays, actuators, electrostatic shields, electromagnetic shields, and conductive coatings has been actively undertaken.
In particular, a significant amount of research into replacing an indium tin oxide (ITO) layer with a conductive polymer has been undertaken in organic solar cells which have been prominent as a replacement energy sources in the era of high oil prices.
With respect to an ITO layer used as a transparent electrode in a typical organic solar cell, since a thin film is formed using a vacuum deposition method, there have been many limitations in terms of a glass transition temperature, a substrate size, and a layer thickness, in the case that the ITO layer is used on a flexible substrate. Also, the ITO layer may be easily delaminated due to rigidity thereof in the case that the flexible substrate is bent, and productivity may be relatively low.
A method of using graphene having a high degree of conductivity and transparency has been proposed in order to replace the ITO layer. However, with respect to the graphene, a sintering temperature thereof may be relatively high, at 1000° C. or more, and the graphene may be difficult to form across a relatively large area.
In contrast, with respect to the conductive polymer, a transparent electrode having a relatively large area may be easily and quickly prepared, because there may be no limitation on the selection of a substrate, a heat treatment temperature may be low, and a solution process may be possible. Therefore, research into using a conductive polymer as a transparent electrode for replacing an ITO layer, a transparent electrode material of an organic solar cell, has recently been actively conducted.
In general, in the case that an organic solar cell is formed across a relatively large area, it is important that the organic solar cell is realized at a low cost. For this purpose, a printing method, such as spray coating, gravure offset printing, inkjet printing, or screen printing, is mainly considered instead of typically used spin coating.
In particular, since a method of using inkjet printing may form a pattern in a desired area by using a small amount of a material and digital patterning may be possible without using a separate negative plate, productivity may be improved in the case that an organic solar cell is formed across a relatively large area. Also, it is also important that the patterning be completed in a short period of time in order to prepare the organic solar cell having a large area, wherein this may be satisfied if the inkjet printing method is used. Therefore, research into methods of using inkjet printing in a process of preparing an organic solar cell has recently been actively undertaken.
However, in the case in which a conductive polymer is used in inkjet printing, since the surface tension of the conductive polymer is high, the conductive polymer may be difficult to be used as it is for inkjet printing. Jetting may be possible if a surfactant is added to overcome the above limitation, but the spreadability of an ink may not be sufficient, and thus, a line may be disconnected during the formation of a line pattern. Also, in the case that an organic solvent having low surface tension is added in order to address the above limitation, jetting properties may deteriorate or the conductivity of a solution may decrease. Therefore, with respect to inkjet compositions using conductive polymers developed so far, the spreadability thereof may be low and the surface tension thereof may be high, and thus, the inkjet compositions may not be suitable for a process of preparing an organic solar cell by using an inkjet printing method.
Therefore, development of a conductive polymer ink composition having excellent coating properties of a photoactive layer as well as facilitating the formation of a transparent electrode able to replace a typical ITO layer during the preparation of an organic solar cell due to excellent spreadability is urgently required.